Papal conclave has roots in turbulent 13th century

VATICAN CITY (Reuters) - When Roman Catholic cardinals enter the secret conclave to choose a new pope on Tuesday they will be following a ritual dating to the 13th century, when papal elections could last for years and some cardinals died during the grueling process.

The term conclave comes from the Latin for "with a key" and refers to the practice of locking cardinals away from the world's prying eyes to allow them to choose a new pope without outside interference.

The 115 cardinal-electors will disappear from public view on Tuesday to vote in the Sistine Chapel for a successor to Pope Benedict as leader of the world's 1.2 billion Roman Catholics.

A puff of white smoke from a Vatican chimney, signifying a decision has been reached, is expected within a few days if the conclaves of the past 100 years are any guide.

It was not always that straightforward.

The election of Gregory X in September 1271, at a time when the Church was riven by political divisions, came after almost three years of deliberations in the town of Viterbo, 85 km (50 miles) north of Rome.

After two inconclusive years, frustrated locals rioted, removed the roof from the palace where the cardinals were gathered - supposedly to let the Holy Spirit join them - and cut back their food supplies to spur them to break the deadlock.